Symmetrical or asymmetrical signals may be transmitted in various circuits. In this case, symmetrical signals are also understood as being “differential” or “balanced to ground” signals. Asymmetrical signals are also called “single ended” or “unbalanced to ground” signals.
For symmetrical signal routing, each conductor is assigned a second conductor of the same design (e.g., the two conductors occur in pairs and may be twisted with one another). The signals have a phase difference of 180°. Interference caused by radio signals or magnetic fields may then have virtually the same effect on both wires (e.g., common mode signal). The useful signal (e.g., push-pull signal) may be obtained in the receiver by determining the voltage difference between the two lines. During this determination, a common mode interference signal, equally present on both lines, emerges again. In contrast, irradiated interference affects only one conductor during asymmetrical transmission since the return conductor is the system ground. Therefore, the interference may not be removed by forming a 180° phase difference in the same manner.
Some applications may require conversion of symmetrical signals into asymmetrical signals or vice versa. For this purpose, as known from DE 101 04 260 A1, a Boucherot bridge, such as described in DE 102011005349 A1, the older German application 102013209450.7, or in H. Meinke, F. W. Gundlach: “Taschenbuch der Hochfrequenztechnik” [Pocket book of high-frequency technology], Springer Verlag, 3rd edition, 1968, pages 1437-1438, may be used.
Such a Boucherot bridge substantially consists of two discrete circuitry conduction paths, one path (e.g., high-pass branch) that effects a forward rotation in terms of phase by 90° and one path (e.g., low-pass branch) that effects a backward rotation in terms of phase by 90°. The conventional Boucherot bridge is generally used to generate a symmetrical signal from an asymmetrical signal or vice versa. However, the conventional Boucherot bridge is narrow-band since the voltages with respect to ground appearing at the output or input ports of the Boucherot bridge are exactly identical in magnitude at only a single frequency. Thus, the signals may be converted from symmetrical to asymmetrical or vice versa only in a narrow frequency range.
Some balancing applications require a broader frequency band. Broadband applications in magnetic resonance imaging (MRI), may use transformers (e.g., line transformers such as baluns) for circuits intended to be used for two or more field strengths. Thus, for example, two decades of bandwidth may be covered by wound cores of ferrite. Ferrites fail in magnetic fields (e.g., in the patient area of an MRI system) since ferrites saturate. Therefore, the transformer is composed of air-coupled windings. Such components are not usually customary on the market but are made to order and are therefore relatively expensive and difficult to produce.